[quote author="LiveAndWorkInIrvine" date=1249617203][quote author="Geotpf" date=1249596462]Most For Sale By Owner sales aren't on the MLS. A good place to find all sales is Redfin.com, which lists MLS sales as well as FSBOs off of Zillow, Oodle, and several other websites, as well as bank-owned REOs that are only on the bank's website and not the MLS. The only major source of listings they don't list is ones off of Craigslist because Craigslist won't let them.</blockquote>
That is the interesting part, I see for sale signs with realtors like Coldwell Banker, etc...but, I cannot find the listings on their websites (or even other real estate websites). I PM'd usctrojanman29 a couple addresses, so hopefully he can help clarify this issue.</blockquote>
It's possible the house isn't officially on the market at the moment. Either it's an REO that the bank hasn't approved the price yet, a house (probably a vacant one) that was once listed but taken off the market for whatever reason, or a recent or pending sale. The Realtors tend to not take down signs until yelled at, because it's like a free mini-billboard for their office. People call the number on the sign, and the Realtor will go, "That one is in escrow (or whatever), but I have another one just like it for sale over here yatta yatta".
Edit: Or it might be a "pocket listing". Sometimes Realtors hold back houses and don't put it on the MLS, at least not at first-they only show it to their existing clients first. There are a lot of theoretical reasons for this, but in the real world the main one is so the Realtor can get double commission (because he's representing both the buyer and seller)-he's being greedy.